LPC.H

The public symbol file NTKRPAMP.PDB for the original release of Windows 10 tells that the kernel is built with the LPC.H header at

d:\th\minkernel\ntos\inc

and draws from it the following type definitions:

Line Number Type
104 struct _LPC_MESSAGE
115 struct _LPCP_NONPAGED_PORT_QUEUE
121 struct _LPCP_PORT_QUEUE
148 struct _LPC_PORT_OBJECT

The header LPC.H is not known in any Device Driver Kit (DDK) or Windows Driver Kit (WDK).